Atlanta Braves’ Jason Heyward, is helped by New York Mets catcher John Buck and umpire Greg Gibson after being hit by a pitch thrown by New York Mets’ Jonathon Niese during the sixth inning at Citi Field on Wednesday in New York.

NEW YORK — Citi Field has been a danger zone for the Atlanta Braves this summer.

Jason Heyward sustained a broken right jaw when he was hit by a pitch Wednesday, becoming the second key member of the NL East leaders to go down with a scary injury at the New York Mets’ ballpark. Veteran pitcher Tim Hudson broke his ankle last month on a gruesome play at first base, ending his season.

“It’s just a fluke thing that it’s happened twice here,” Chris Johnson said after his three-run homer in the 10th inning sent Atlanta to a 4-1 victory.

Heyward went down in a heap during a frightening scene in the sixth. With blood in his mouth, he was examined by Mets doctors and taken to a hospital for X-rays.

He was diagnosed with two fractures in his jaw and will undergo surgery Thursday in Atlanta. The team said it will have an estimated timetable for his return after the operation.

Heyward’s grandparents were at Citi Field and accompanied him to the hospital, along with trainer Jeff Porter. Heyward and Porter stayed behind in New York as the Braves traveled to St. Louis for a four-game series that begins Thursday night.

Heyward was expected to fly to Atlanta on Wednesday night.

“He never lost consciousness,” manager Fredi Gonzalez said. “Right before he went to the hospital he popped his head into the clubhouse to say goodbye to some of the guys.

“It’s not the ballpark, it’s just a matter of freak stuff happening. It can happen anywhere.”

Atlanta, with baseball’s best record and a huge division lead, got an RBI single from Freddie Freeman, and another impressive start by rookie Alex Wood in splitting the two-game series for its 20th victory in 24 games. The Braves also benefited from a disputed call in the 10th.

Andrelton Simmons singled off Scott Atchison (3-2) with two outs, and Freeman hit a two-strike grounder back toward the box that ticked off the bottom of Scott Rice’s glove and rolled behind him. The reliever retrieved the ball and fired to first, where Freeman was called safe.

Mets manager Terry Collins came out to argue with umpire Jerry Layne. Johnson then launched a drive to left field on Greg Burke’s first big league pitch since he was recalled from the minors Sunday.

“We were trying to come in there on Chris. We’d been doing it all game. It was basically where I wanted to put it,” Burke said. “It was up a little bit. I went back and looked, it was off the plate, but I guess there’s a reason why the guy’s hitting .300.”

Johnson, who began the day second in the NL in batting at .334, struck out his previous three times up.

By the time Johnson crossed the plate, Layne had ejected New York second baseman Daniel Murphy. Collins came out for a more vehement argument this time, tossed his hat to the ground and was thrown out by Layne, as well.

“We had a difference of opinion,” Murphy said. “Right or wrong, I’d prefer not to get thrown out right there. But I think tensions were running high and mine boiled over.”

Collins walked back to the dugout without retrieving his cap, leaving it there in the dirt by Layne’s feet.

“Jerry just said he thought he got it right. I didn’t have much to say that was very nice,” Collins said. “I went out to protect Murph. I couldn’t get him back in the game, so I might as well come up with him.”

The crowd of 22,935 gave Layne a derisive cheer when he called a Mets runner safe in the bottom of the 10th.

Luis Avilan (5-0) pitched out of a bases-loaded jam in the ninth, and Craig Kimbrel reached 40 saves for the third straight season. He has converted 30 chances in a row, extending his club record.

Simmons and Freeman each had three hits.

Josh Satin homered for the Mets, and Jonathon Niese struck out a season-high nine for the second consecutive start. Rookie center fielder Juan Lagares turned in his latest defensive gem with an outstanding throw to cut down Simmons trying to stretch a one-out single in the fourth, Atlanta’s first hit off Niese.

Heyward was struck by a 90 mph fastball from Niese in the sixth. The impact made a loud noise, and the crowd groaned as Heyward crumpled to the ground.

He stayed down on his back for about three minutes before getting helped to his feet. Heyward walked slowly off the field under his own power, escorted by a trainer, and was replaced by Jordan Schafer.

Visibly concerned, Niese tapped himself with his glove as Heyward walked off, and Heyward appeared to acknowledge him.

“I wanted to elevate a fastball but it just kind of ran in on him. Obviously no intent,” Niese said. “I felt horrible. This game can be pretty dangerous.”

Perhaps a bit shaken, Niese then gave up singles to Simmons and Freeman in a three-pitch span as Atlanta tied it at 1.

On a tear at the plate since moving into the leadoff spot last month, Heyward is batting .253 with 13 homers and 37 RBIs. The right fielder won a Gold Glove last season and was an All-Star as a rookie in 2010.

“It was tough. It caught him in a bad spot. We’ll just have to wait and hear how he is,” Wood said.

NOTES: Gonzalez said infielder Elliot Johnson, released Tuesday by Kansas City, will join the Braves in St. Louis. “We’re obviously going to be making some roster moves,” the manager said. ... Braves OF Justin Upton missed the series with a strain in his upper back. He said he thinks he will be ready for the St. Louis series. ... Upton’s brother, B.J., started in CF on his 29th birthday. He went 0 for 4 with two strikeouts and is hitless in his last 24 at-bats. ... Johnson batted cleanup for the second time this season. ... Wood went six innings in his seventh major league start — three against the Mets. ... Satin has reached base safely in all 29 of his starts this season, the fourth-longest streak in the NL.